A 5-cm-long Er/Yb co-doped all-fiber laser is studied. Two fiber Bragg gratings (FBGs) are written in the Er/Yb co-doped sensitive fiber using UV beams. A 980 nm pumping laser diode (LD) is used, and output wavelength is selected by two FBGs. The single-frequency laser is achieved at 1544.68 nm. The 3 dB spectrum width is 0.08 nm, while the side mode suppression ratio is 55 dB. The maximum output power exceeds 4 mW for pump power of 140mW and the stability is less than ± 0.01 dB. Single-frequency operation is verified using a scanning Fabry-Perot (F-P) interferometer. Relative intensity noise is less than - 100 dB. A 10 Gbit/s code rate is used in the fiber laser transmission experiment. A good optical eye diagram is received after 21 km single-mode fiber transmission. A simple distributed Bragg reflection (DBR) fiber laser array is designed. The wavelength difference of output laser array is 0.8 nm, conforming to the ITU-T channel spacing standard of wavelength-division multiplexing systems.